One of the problems when processing metals, including aluminum, is the accumulation of inventory during processing and the costs associated with maintaining and storing such inventory. These problems are most significant during the production of aluminum sheet through conventional ingot metallurgy. In conventional ingot processing, multiple processing lines are required to take the cast ingot to its final form of annealed coiled product, with inventory capacity required for nearly every intermediary product form. For ingot processing, these processing steps include: casting; homogenizing; hot rolling; intermediate annealing; cold rolling (roughing mill); cold rolling (finish mill); and coil annealing. When the ingot is cast, the ingots are inventoried prior to re-heating to the homogenization treatment. When the ingot is hot rolled, the hot rolled coils are stored prior to further processing. Similarly, cold rolled coils also require storage prior to the cold roll finishing pass and annealing processing steps.
Much of the inventory problem created by ingot casting has been solved through the use of continuous casting followed by in-line hot rolling. This processing method eliminates the re-heating of ingots and the inventory problem associated with storing the ingots prior to homogenization. However, inventory problems still exist in connection with the secondary processing of aluminum. That is, once the cast product is hot rolled, the hot rolled coils must still be stored prior to further processing. As such, a need has developed to provide improved apparatus and processing techniques to overcome the drawbacks associated with present day processing.
The invention solves this problem by combining continuous casting, direct hot rolling and induction heating of non-heat treatable aluminum alloy products into a single production line. With the invention, a final annealed product is produced in coiled form without the production of intermediate product forms. Additionally, this process significantly reduces energy consumption used in the annealing step by exploiting the residual latent heat of the hot rolled product in the annealing process.
The use of induction heating for aluminum alloys alone is known. U.S. Pat. No. 5,739,506 to Hanton et al. discloses an example of an induction heating system which relates to transverse flux heating. These heating systems are desirable when treating a variety of widths of strip or sheet metal.
Induction heating and processing of aluminum is also disclosed in U.S. Pat. No. 5,562,784 to Nishikawa et al. This patent is directed to an aluminum alloy substrate for electrolytically grainable lithographic printing plate. In making this material, the aluminum alloy is continuously cast. The cast material can then be either cold rolled or hot rolled and cold rolled. The substrate is heat treated for recrystallization in the course of cold rolling. The heat treatment is disclosed as either a continuous annealing furnace or a transverse flux induction heating. The induction heating of Nishikawa et al. is associated with recrystallization after cold rolling and is not part of an apparatus or method which continuously casts, hot rolls and inductively heats a non-heat treatable aluminum alloy into a final annealed product.